Pattern-based compilation of asynchronous consumption

ABSTRACT

The present invention extends to methods, systems, and computer program products for transforming source code to await execution of asynchronous operations. Embodiments of the invention simplify authoring and use of asynchronous methods, by generating statements that use well-defined awaitable objects to await completion of asynchronous operations. For example, a computer system can transform a statement that requests to await the completion of an asynchronous operation into a plurality of statements that use a predefined pattern of members of an awaitable object corresponding the asynchronous operation. The pattern can include one or more members configured to return a completion status of the asynchronous operation, one or more members configured to resume execution of the asynchronous method at a resumption point when the asynchronous operation completes, and one or more members configured to retrieve completion results. Accordingly, the plurality of statements can use these members to await execution of the asynchronous operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

BACKGROUND 1. Background and Relevant Art

Computer systems and related technology affect many aspects of society.Indeed, the computer system's ability to process information hastransformed the way we live and work. Computer systems now commonlyperform a host of tasks (e.g., word processing, scheduling, accounting,etc.) that prior to the advent of the computer system were performedmanually. More recently, computer systems have been coupled to oneanother and to other electronic devices to form both wired and wirelesscomputer networks over which the computer systems and other electronicdevices can transfer electronic data. Accordingly, the performance ofmany computing tasks are distributed across a number of differentcomputer systems and/or a number of different computing environments.

Authoring computer applications that perform some computing taskspresent unique challenges for programmers. Applications are generallybroken down into one or more tasks which execute in a well-defined,sequential program control flow. A problem arises when tasks, whichcould otherwise be performing other functions, must wait for completionof operations having high latency. For example, an application mayimplement a task for that generates a user interface. At some pointduring execution, the user interface task may require information thatis not yet available, request the information (e.g., via a method call),and then block while waiting for the information to become available. Inthis circumstance, the user interface would “freeze” or becomeunresponsive while the user interface task blocks to wait for theinformation to become available. For requests that return theinformation quickly, blocking may not present a serious problem.However, for requests with high levels of latency (e.g., requests thatare computationally intensive, or requests for information from othercomputing systems), blocking can lead to serious performance issues. Notonly can blocking make interactive applications unresponsive, blockingcan hurt the scalability and performance of any application.

To address the performance penalty incurred by blocking, asynchronousprogramming techniques have been developed, which allow tasks tocontinue executing while awaiting the return of asynchronous requests ormethods. Asynchronous programming has, however, been challenging whenusing mainstream programming languages. To achieve asynchrony,developers are forced to write asynchronous methods that respond torequests for “callbacks,” requested by a calling context. Developers arefurthermore forced to write asynchronous methods that track state ofasynchronous operations themselves. As such, authoring asynchronousmethods is typically infeasible for all but the most advanceddevelopers.

BRIEF SUMMARY

The present invention extends to methods, systems, and computer programproducts for transforming source code to await execution of asynchronousoperations. In some embodiments, a computing system accesses anasynchronous method from within a portion of computer program sourcecode, and recognizes a statement within the asynchronous methodrequesting to await the completion of an asynchronous operation. Thecomputer system then transforms the statement into a plurality of otherstatements, which are configured to use an awaitable object to awaitcompletion of the asynchronous operation.

More specifically, the other statements are configured to first use afirst member of the awaitable object to determine a completion status ofthe asynchronous operation. When the completion status indicates thatthe asynchronous operation has not already completed, the otherstatements are configured to use a second member of the awaitable objectto await completion of the asynchronous operation, and to resumeexecution of the asynchronous method at a resumption point in theasynchronous method when the asynchronous operation completes. The otherstatements are also configured to return to a calling context afterawaiting completion of the asynchronous operation, to resume executionof the asynchronous method at the resumption point subsequent tocompletion of the asynchronous operation, and to use a third member ofthe awaitable object to access a result of the asynchronous operationsubsequent to resuming execution of the asynchronous method.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by the practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered to be limiting of its scope, the invention will bedescribed and explained with additional specificity and detail throughthe use of the accompanying drawings in which:

FIG. 1 illustrates an example computer architecture that facilitatestransforming source code to await execution of asynchronous operations.

FIG. 2 illustrates a flow chart of an example method for transformingsource code to await execution of asynchronous operations.

DETAILED DESCRIPTION

The present invention extends to methods, systems, and computer programproducts for transforming source code to await execution of asynchronousoperations. In some embodiments, a computing system accesses anasynchronous method from within a portion of computer program sourcecode, and recognizes a statement within the asynchronous methodrequesting to await the completion of an asynchronous operation. Thecomputer system then transforms the statement into a plurality of otherstatements, which are configured to use an awaitable object to awaitcompletion of the asynchronous operation.

More specifically, the other statements are configured to first use afirst member of the awaitable object to determine a completion status ofthe asynchronous operation. When the completion status indicates thatthe asynchronous operation has not already completed, the otherstatements are configured to use a second member of the awaitable objectto await completion of the asynchronous operation, and to resumeexecution of the asynchronous method at a resumption point in theasynchronous method when the asynchronous operation completes. The otherstatements are also configured to return to a calling context afterawaiting completion of the asynchronous operation, to resume executionof the asynchronous method at the resumption point subsequent tocompletion of the asynchronous operation, and to use a third member ofthe awaitable object to access a result of the asynchronous operationsubsequent to resuming execution of the asynchronous method.

Embodiments of the present invention may comprise or utilize a specialpurpose or general-purpose computer including computer hardware, suchas, for example, one or more processors and system memory, as discussedin greater detail below. Embodiments within the scope of the presentinvention also include physical and other computer-readable media forcarrying or storing computer-executable instructions and/or datastructures. Such computer-readable media can be any available media thatcan be accessed by a general purpose or special purpose computer system.Computer-readable media that store computer-executable instructions arecomputer storage media (devices). Computer-readable media that carrycomputer-executable instructions are transmission media. Thus, by way ofexample, and not limitation, embodiments of the invention can compriseat least two distinctly different kinds of computer-readable media:computer storage media (devices) and transmission media.

Computer storage media (devices) includes RAM, ROM, EEPROM, CD-ROM orother optical disk storage, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to store desiredprogram code means in the form of computer-executable instructions ordata structures and which can be accessed by a general purpose orspecial purpose computer.

A “network” is defined as one or more data links that enable thetransport of electronic data between computer systems and/or modulesand/or other electronic devices. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or a combination of hardwired or wireless) to acomputer, the computer properly views the connection as a transmissionmedium. Transmissions media can include a network and/or data linkswhich can be used to carry or desired program code means in the form ofcomputer-executable instructions or data structures and which can beaccessed by a general purpose or special purpose computer. Combinationsof the above should also be included within the scope ofcomputer-readable media.

Further, upon reaching various computer system components, program codemeans in the form of computer-executable instructions or data structurescan be transferred automatically from transmission media to computerstorage media (devices) (or vice versa). For example,computer-executable instructions or data structures received over anetwork or data link can be buffered in RAM within a network interfacemodule (e.g., a “NIC”), and then eventually transferred to computersystem RAM and/or to less volatile computer storage media (devices) at acomputer system. Thus, it should be understood that computer storagemedia (devices) can be included in computer system components that also(or even primarily) utilize transmission media.

Computer-executable instructions comprise, for example, instructions anddata which, when executed at a processor, cause a general purposecomputer, special purpose computer, or special purpose processing deviceto perform a certain function or group of functions. The computerexecutable instructions may be, for example, binaries, intermediateformat instructions such as assembly language, or even source code.Although the subject matter has been described in language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the described features or acts described above.Rather, the described features and acts are disclosed as example formsof implementing the claims.

Those skilled in the art will appreciate that the invention may bepracticed in network computing environments with many types of computersystem configurations, including, personal computers, desktop computers,laptop computers, message processors, hand-held devices, multi-processorsystems, microprocessor-based or programmable consumer electronics,network PCs, minicomputers, mainframe computers, mobile telephones,PDAs, pagers, routers, switches, and the like. The invention may also bepracticed in distributed system environments where local and remotecomputer systems, which are linked (either by hardwired data links,wireless data links, or by a combination of hardwired and wireless datalinks) through a network, both perform tasks. In a distributed systemenvironment, program modules may be located in both local and remotememory storage devices.

FIG. 1 illustrates an example computer architecture 100 that facilitatestransforming source code to await execution of asynchronous operations.Referring to FIG. 1, computer architecture 100 includes compiler 101.Each of the depicted components is connected to one another over (or ispart of) a network, such as, for example, a Local Area Network (“LAN”),a Wide Area Network (“WAN”), and even the Internet. Accordingly, each ofthe depicted components as well as any other connected computer systemsand their components, can create message related data and exchangemessage related data (e.g., Internet Protocol (“IP”) datagrams and otherhigher layer protocols that utilize IP datagrams, such as, TransmissionControl Protocol (“TCP”), Hypertext Transfer Protocol (“HTTP”), SimpleMail Transfer Protocol (“SMTP”), etc.) over the network.

Compiler 101 is configured to process source code (e.g., source code105) to represent and support execution of various programming elements.More particularly, compiler 101 is configured to support the compilationof asynchronous methods (e.g., asynchronous method 106) that areconfigured to await the execution of one or more asynchronousoperations. Asynchronous operations may be executed in connection withan awaitable object (e.g., awaitable object 109) that exposes apredescribed pattern (e.g., one or more members 110-112 for interactingwith the awaitable object and/or the asynchronous operation(s)) and thatmanages execution of the asynchronous operations (e.g., as part of astate machine). Authors of asynchronous methods can thus include one ormore statements (e.g., statement 107) that “await” awaitable objects.The compiler 101 can then transform the “await” statements into one ormore other statements that use the predescribed pattern of the awaitableobject to await completion of the asynchronous operation(s) andreport/propagate results.

Compiler 101 can include hardware and/or software components thattransform a source computing language into a destination computinglanguage. For example, compiler 101 can translate “higher-level” sourcecode of a programming language (e.g., C#, VISUAL BASIC, JAVA,JAVASCRIPT, etc.) into “lower-level” instructions (e.g., assemblylanguage/machine code, intermediate language code, etc.). Theinstructions can then be executed by one or more physical and/or virtualcomputing systems, by one or more managed runtime environments, etc. Thelower-level instructions can also be subject to further processing ortranslation. Compiler 101 can, in some embodiments, be configured toreceive and transform source code for a variety of programming languagesinto one or more types of lower-level instructions. In otherembodiments, compiler 101 can be configured to translate source code ofa single programming language into a single type of lower-levelinstructions.

Compiler 101 can be configured with one or more modules that access andprocess source code. In some embodiments, the modules can includeaccessor module 102, recognizer module 103, and transformation module104. Of course, one will recognize in view of the disclosure herein thatcompiler 101 is not limited to the specific arrangement of modulesdescribed, and can perform the inventive embodiments using otherconfigurations.

Accessor module 102 is configured to receive source code which, fromtime to time, can include one or more asynchronous methods that call oneor more awaitable instances. For example, accessor module can beconfigured to access asynchronous method 106 from source code 105.Asynchronous method 106 can include statement 107, which awaits anawaitable instance (e.g., awaitable object 109) that executes one ormore asynchronous operations, and which exposes a predescribed pattern(e.g., members 110-112).

Recognizer module 103 is configured to receive asynchronous methods fromaccessor module 102 and to recognize statements within the methods thatrequest to await the completion of asynchronous operations throughinstances (e.g., awaitable objects) that expose the predescribedpattern. For example, recognizer module can be configured to identifystatement 107 through the use of an express keyword, such as ‘await’.Statement 107 may therefore include syntax similar to ‘await t’, where‘t’ is an awaitable object, or an instance thereof (e.g., a clockobject). Recognizer module 103 can accordingly recognize that theasynchronous method 106 containing the statement 107 requests to use apredescribed pattern exposed by ‘t’ to await completion of asynchronousoperations of ‘t’. When ‘t’ represents a clock object, for example, ‘t’can be “awaited on” until an asynchronous operation of the clock objectcompletes (e.g., until “the clock strikes noon”). Of course, the ‘await’keyword is exemplary only, and use of virtually any keyword is possible.In some embodiments, no express keyword is used, and the statement 107is recognized implicitly based on context of the statement 107 withinsurrounding code.

Transformation module 104 is configured to receive statement 107 fromrecognizer module 103 and to transform statement 107 into one or moreother statements that are configured to cause the asynchronous method106 use the awaitable object 109 to await asynchronous operation(s).Transformation module 104 typically generates a plurality of statements113 that use the predefined pattern (e.g., a well-defined set ofmembers, such as methods) exposed by awaitable objects. Awaitableobjects (e.g., awaitable object 109) can be awaitable, at least in part,by virtue of exposing the predefined pattern and by managing executionof asynchronous operations (as part of a state machine, for example). Inone or more embodiments, the pattern can define a plurality of members(e.g., methods) 110, 111, and 112 for awaitable objects to expose. Itwill be appreciated in view of this disclosure that the particularnumber of members and their corresponding function can be modifiedwithout departing from the scope of the invention.

Transformation module 104 can be configured to generate first statements113 that are, in turn, configured to use member 110 to determine acompletion status of the asynchronous operation(s). Member 110 cancomprise a first method (e.g., ‘IsCompleted’) of the awaitable object109 that is configured to return a completion status of the asynchronousoperation(s) associated with the awaitable object. The completion statuscan comprise, for example, a Boolean value that is TRUE when theasynchronous operation(s) have completed, or that is FALSE when theasynchronous operation(s) have not yet completed. Any other appropriatemeans for communicating completion status is also possible, however(e.g., string values, integer values, objects, etc.).

It will be appreciated that, even if member 110 is called immediatelysubsequent to initialization (by the synchronous method or otherwise) ofan awaitable object, the asynchronous operation(s) associated with theawaitable object may already be completed before member 110 is called.Therefore, an optimization is achieved by configuring the transformationmodule 104 to generate the first statements 113 that, prior to settingup any environment or state needed to do the awaiting, use member 110 todetermine whether the asynchronous operation(s) need to be awaited. Theasynchronous operation(s) may already be completed because there was nowork to be done by the operation(s), the operation(s) completedexceptionally, etc. Accordingly, the transformation module 104 can beconfigured to generate statements (not shown) that retrieve/propagateresults of the asynchronous operation(s) (using member 112, for example,as discussed later) if the asynchronous operation(s) have alreadycompleted.

Otherwise, if the asynchronous operation(s) are not yet complete, thetransformation module 104 can be configured to generate secondstatements 113 that perform initialization tasks and “pre-await” work,including setting up environment or state that supports suspension andresumption of the asynchronous method 106. For example, the secondstatements 113 can be configured to set up a resumption point (e.g., alabel) in the asynchronous method 106 where execution of theasynchronous method 106 can resume when the asynchronous operation(s)complete and any appropriate “post-await” work can be performed. Thisresumption point can be associated with a resumption delegate that canbe used to identify and resume execution at the resumption point.Initialization and “pre-await” work can include, for example,initialization of a ‘resumption’ delegate on first use, setting uprelevant data structures that enable the later resumption, spillinglocals to the heap and then pulling them back onto the stack afterresumption, and the like.

After generating second statements 113 configured to perform “pre-await”work, such as establishing and initializing environment or state data,the transformation module 104 can be configured to generate thirdstatements 113 that use member 111 to await completion of theasynchronous operation(s) by configuring a resumption delegate. Member111 can be a second method (e.g., ‘OnCompleted’) of the awaitable object109 configured to set the resumption delegate on the awaitable object109. Setting the resumption delegate can involve configuring theawaitable object 109 to use the resumption delegate to resume executionof the asynchronous method 107 at the resumption point when theasynchronous operation(s) complete. Member 111 can therefore beconfigured take as a parameter the resumption delegate, configure theawaitable object 109 and return (e.g., return TRUE when the resumptiondelegate is set properly).

After successfully using member 111 to set the resumption delegate, thetransformation module 104 can be configured to generate fourthstatements 113 that cause the asynchronous method 106 to return to acalling context (e.g., to exit asynchronous method 106 and to return tothe calling context in source code 105). Thus, while the asynchronousoperation(s) complete, the asynchronous method can be suspended and codewithin source code 105 can be executed concurrently with theasynchronous operation(s).

When the asynchronous operation(s) complete, execution of theasynchronous method 106 can resume at the resumption point where anyappropriate “post-await” work is performed and/or results of theasynchronous operation(s) are obtained. For instance, fifth statements113 can be configured to establish the resumption point (e.g., a label).The transformation module 104 can be configured to generate sixthstatements 113 that then use member 112 to retrieve/propagate results ofthe asynchronous operation(s), as well as any other appropriatestatements for performing other “post-await” work. Member 112 can be athird method (e.g., ‘GetResult’) of the awaitable object 109 configuredto return or propagate results of the completion of the asynchronousoperation(s). Results can include, for example, result data (when theasynchronous operation(s) complete successfully), exception data (whenthe asynchronous operation(s) complete exceptionally), and cancellationdata such as a stored token indicating the source of a cancellationrequest (when the asynchronous operation(s) complete due tocancellation).

The results obtained via member 112 can then be returned by theasynchronous method 106 to a calling context, or otherwise propagated bythe asynchronous method 106. Through use of the member 112, theawaitable object 109 can be seen as a “future” object that can be usedto retrieve the future or eventual results of asynchronous operations.In some embodiments, however, the awaitable object 109 can also be usedto obtain intermediary results (in addition to mere completion status).

As indicated above, the particular number and function of the members ofthe predefined pattern can vary. For example, in one embodiment, theremay be only two members. The first member (e.g., BeginAwait), forexample, can be configured to combine the functionality of members 110and 111. For example, the first member can be called with a resumptiondelegate, much like member 111, but can also report status, much likemember 110. If the asynchronous operation(s) have completed, the membercan be configured to simply return (e.g., return FALSE). If theasynchronous operations have not completed, the member can be configuredto set the resumption (much like member 111) and return (e.g., returnTRUE). The second member (e.g., EndAwait) can function substantiallysimilar to member 112, and be usable to retrieve/propagate results ofthe completion of asynchronous operations. One will appreciate that whenusing this alternative pattern of members, the statement 113 can setstate before calling any members. One will also appreciate that thisalternative pattern can also be created by mere use of the three memberspreviously described. For instance, awaitable object 109 can expose thefirst member, but use the first member to call member 110 and member110.

While asynchronous object 109 can include instances (e.g., an instanceresulting from instantiating an object), it will be appreciated that, insome embodiments and in some programming languages, the indirection ofinstantiating an object may not be necessary. It will also beappreciated that the embodiments described herein are usable using bothstatic binding and dynamic binding. Furthermore, one will recognize thatthe embodiments described herein can be applicable to a host ofdifferent types of objects and different programming languageconstructs. Accordingly, awaitable objects can be considered to becomposable objects any applicable to virtually any programming languagesupported construct.

Embodiments described herein thus enable the authoring of asynchronousmethods that can simply await awaitable objects that expose a predefinedpattern and that manage execution of asynchronous operations. This freesthe developer from worrying about details surrounding use ofasynchronous operations, letting the compiler 101 and asynchronousobjects take care of these details.

FIG. 2 illustrates a flow chart of an example method 200 fortransforming source code to await execution of asynchronous operations.Method 200 will be described with respect to the components and data ofcomputer architecture 100 depicted in FIG. 1.

Method 200 includes an act of accessing an asynchronous method fromwithin a portion of computer program source code (act 201). For example,accessor module 102 can access at least a portion of source code 105.Source code 105 can include asynchronous method 106, which can in turninclude one or more statements 107 that requests to await and awaitableinstance (e.g., awaitable object 109). Awaitable object 109 canexecute/manage one or more asynchronous operations, and can expose apredefined pattern, either directly or indirectly.

Subsequent to accessing source code, method 200 includes an act ofrecognizing a statement requesting to await the completion of anasynchronous operation, the statement included in the asynchronousmethod (act 202). For example, recognizer module 103 canidentify/recognize that asynchronous method 106 includes statement 107.Identification can be based on express identifiers (e.g., the keyword‘await’) or implicit indicators (e.g., the context of statement 107within asynchronous method 106).

In response to recognizing the statement, method 200 includes an act oftransforming the statement into a plurality of other statements, theplurality of other statements configured to use an awaitable object toawait completion of the asynchronous operation (act 203). For example,transformation module 104 can transform the statement 107 into aplurality of statements 113 that use the predefined pattern exposed byawaitable object 109 to await completion of asynchronous operations. Theexact form of the statements can vary widely depending on the predefinedpattern, as well as other things. The generated statements illustratedin FIG. 2, for example, use a predefined pattern that includes threemembers. It will be appreciated, however, the embodiments extend to anynumber of members.

As illustrated, method 200 includes the plurality of other statementsbeing configured to use a first member of the awaitable object todetermine a completion status of the asynchronous operation (act 204).For example, transformation module 104 can generate statements that usemember 110 of awaitable object 109 to determine a completion status theasynchronous operation(s). When the member 110 indicates that theoperation(s) are complete, the statements can use member 112 to retrieveresults and to report to a calling context that the asynchronousoperation(s) have completed. Alternatively, when member indicates thatthe operation(s) are incomplete, the statements can set up any state orenvironment needed for suspending the asynchronous method 106, such asestablishing a resumption point (e.g., a label) in the asynchronousmethod 106.

Along these lines, method 200 also includes the plurality of otherstatements being configured to use a second member of the awaitableobject to await completion of the asynchronous operation when thecompletion status indicates that the asynchronous operation has notalready completed, the second member configured to await completion ofthe asynchronous operation and to resume execution of the asynchronousmethod at a resumption point in the asynchronous method when theasynchronous operation completes (act 205). For example, transformationmodule 104 can generate statements that use member 111 of awaitableobject 109 to set up a resumption delegate, which can resume executionof the asynchronous method 106 at a resumption point (e.g., the label).

Method 200 also includes the plurality of other statements beingconfigured to return to a calling context after awaiting completion ofthe asynchronous operation (act 206). For example, transformation module104 can generate statements that return to a calling context of theasynchronous method 106, such as other code in source code 105, forinstance. In this way the asynchronous method 106 is suspended while theasynchronous operation(s) being awaited complete. During this time,other code can execute, such that the calling context using theasynchronous method 106 need not block while awaiting completion of theoperation(s).

Method 200 also includes the plurality of other statements beingconfigured to resume execution of the asynchronous method at theresumption point subsequent to completion of the asynchronous operation(act 207). For example, transformation module 104 can generatestatements that enable asynchronous method 106 to resume execution whenthe asynchronous operations(s) complete. The statements can include, insome embodiments, the label corresponding to the previously configuredresumption point. Thus, then when the asynchronous operation(s)complete, the awaitable object 109 can use the resumption delegate(which was previously used in connection with member 111) to resumeexecution at the label.

Method 200 also includes the plurality of other statements beingconfigured to use a third member of the awaitable object to access aresult of the asynchronous operation subsequent to resuming execution ofthe asynchronous method (act 208). For example, transformation module104 can generate statements that use member 112 of awaitable object 109to retrieve results of the completion of the asynchronous operation(s).Asynchronous operation(s) may complete in various contexts, such assuccessful completion, exceptional completion, completion due tocancellation, etc. Accordingly, retrieving results can includeretrieving result data (for successful completion), exception data (forexceptional completion), cancellation data (for completion due tocancellation), and the like.

The embodiments will now be described in the context of exemplarycomputer program pseudo code. It will be appreciated that the pseudocode examples provided are for illustrative purposes only, and are in noway limiting to the applicability of the embodiments described herein.Embodiments are extendable to a variety of computer programminglanguages, far beyond the scope of the foregoing examples.

In some embodiments, asynchronous method 106 may include a statement 107similar to:

TResult result=await t;

Thus, the statement requests to await an awaitable object ‘t’, theresults of which are to be stored in a ‘result’ of type ‘TResult’.Awaitable object ‘t’ can execute/manage one or more asynchronousoperations, and can conform to the predefined pattern (i.e., exposemembers 110-112).

After accessor module 102 and recognizer module 103 access and recognizethe statement, transformation module 104 can transform the statementinto a plurality of statements similar to:

if (t.IsCompleted) { state = Label; t.OnCompleted(continuation); return;Label: } TResult result = t.GetResult( );The statements first check to see whether the asynchronous operation(s)have already completed using the first member 110 (IsCompleted), and ifso, they retrieve results of the operation(s) using the third member 112(GetResult). Otherwise, the statements set up state, configure thecontinuation using the second member 111 (OnCompleted), and return(thereby suspending the asynchronous method). Later, when theoperation(s) complete, execution resumes at ‘Label’ and results ofoperation are retrieved using the third member 112 (GetResult).

While the illustrated pseudo code uses the awaitable object ‘t’directly, embodiments also include levels of indirection, such as byobtaining an ‘awaiter’ from ‘t’ and using the ‘awaiter’. For instance:

var $awatier=t.GetAwaiter( );

In which case the statements would use ‘awaiter’ instead of ‘t’:

!$awaiter.IsCompleted( ); !$awaiter.OnCompleted(continuation);!$awaiter.GetResult( );

It is noted that the statements can be embodied in other forms as well.For example, the statement ‘TResult result=await t;’ may alternativelybe transformed into a plurality of statements that do additional“pre-await” and “post-await” work, as well as other initializationtasks. For instance:

var $awaiter = t.GetAwaiter( ); if (!$awaiter.IsCompleted) { if(IsFirstNotCompletedAwait) { FirstYieldInitialization( ); }PreAwaitWork( ); state = Label; $awaiter.OnCompleted(MoveNextDelegate);PostOnCompletedWork(IsFirstNotCompletedAwait); return; Label:PostAwaitWork( ); } TResult result = $awaiter.GetResult( );

Here, the statements (which use a level of indirection through $awaiter)can potentially perform additional initialization tasks usingFirstYieldInitialization (e.g., if this is the first time thisparticular task is being awaited), and also includes statements doingwork prior to and after awaiting (e.g., PreAwaitWork and PostAwaitWork).As mentioned, these statements can initialize the resumption delegate(MoveNextDelegate) on first use, set up relevant data structures used toenable the later resumption, spill locals to the heap and then pull themback onto the stack after resumption, etc.

In addition, these statements also include PostOnCompletedWork that isperformed after setting the resumption delegate and prior to returningto the calling context. The PostOnCompletedWork gives the compiler anopportunity to do work after the awaitable object has been told it'syielding, which can be work not performed as part of the PreAwaitWork.For example, the PostOnCompletedWork can be used to capture ambientstate (e.g., state connected with the OnCompleted call), remove theambient state prior to the “return” so that the calling context does notsee the ambient state, and then make the ambient state available for theGetResult call.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrativeand not restrictive. The scope of the invention is, therefore, indicatedby the appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed:
 1. At a computer system including one or moreprocessors and system memory, the computer system also including one ormore modules for converting source code into executable code, a methodfor transforming source code to await execution of asynchronousoperations, the method comprising: an act of accessing an asynchronousmethod from within a portion of computer program source code; an act ofrecognizing a statement requesting to await the completion of anasynchronous operation, the statement included in the asynchronousmethod; in response to recognizing the statement, an act of transformingthe statement into a plurality of other statements, the plurality ofother statements configured to use an awaitable object to awaitcompletion of the asynchronous operation, the plurality of otherstatements configured to: use a first member of the awaitable object todetermine a completion status of the asynchronous operation; use asecond member of the awaitable object to await completion of theasynchronous operation when the completion status indicates that theasynchronous operation has not already completed, the second memberconfigured to await completion of the asynchronous operation and toresume execution of the asynchronous method at a resumption point in theasynchronous method when the asynchronous operation completes; return toa calling context after awaiting completion of the asynchronousoperation; resume execution of the asynchronous method at the resumptionpoint subsequent to completion of the asynchronous operation; and use athird member of the awaitable object to access a result of theasynchronous operation subsequent to resuming execution of theasynchronous method.
 2. The method of claim 1, wherein the awaitableobject exposes a single method that calls the first member and thesecond member, the plurality of other statements being configured to usethe single method, instead of using the first member and the secondmember directly.
 3. The method of claim 2, wherein the plurality ofother statements are also configured to initialize state data, includingstate data for the resumption point, prior to calling the single method.4. The method of claim 1, wherein the plurality of other statements arealso configured to initialize state data, including state data for theresumption point, after completion status indicates that theasynchronous operation has not already completed and prior to using thesecond member of the awaitable object to await completion of theasynchronous operation.
 5. The method of claim 1, wherein the pluralityof other statements are also configured to report to the calling contextthat the asynchronous operation has completed when completion statusindicates that the asynchronous operation has already completed, and torefrain from use of the second member.
 6. The method of claim 1, whereinthe plurality of other statements are also configured to obtain theawaitable object by instantiating an instance of the awaitable object.7. The method of claim 1, wherein the result of the asynchronousoperation comprises a result of the asynchronous operation running tocompletion.
 8. The method of claim 1, wherein the result of theasynchronous operation comprises exception data of the asynchronousoperation completing exceptionally.
 9. The method of claim 1, whereinthe result of the asynchronous operation comprises a stored tokenindicating the source of a cancellation request resulting in thecancellation of the asynchronous operation.
 10. The method of claim 1,wherein the awaitable object is a composable object usable for use alongwith all programming language supported constructs.
 11. The method ofclaim 1, wherein the awaitable object is a future object, representingone or more future states of the asynchronous operation running tocompletion, the one or more future states including one or more of:successful completion, exceptional completion, or completion due tocancellation.
 12. A computer program product for use at a computersystem, the computer program product for implementing a method fortransforming source code to await execution of asynchronous operations,the computer program product comprising one or more computer storagemedia having stored thereon computer-executable instructions that, whenexecuted at a processor, cause the computer system to perform themethod, including the following: access an asynchronous method fromwithin a portion of computer program source code; recognize a statementrequesting to await the completion of an asynchronous operation, thestatement included in the asynchronous method; in response torecognizing the statement, transform the statement into a plurality ofother statements, the plurality of other statements configured to use anawaitable object to await completion of the asynchronous operation, theplurality of other statements configured to: use a first member of theawaitable object to determine a completion status of the asynchronousoperation; use a second member of the awaitable object to awaitcompletion of the asynchronous operation when the completion statusindicates that the asynchronous operation has not already completed, thesecond member configured to await completion of the asynchronousoperation and to resume execution of the asynchronous method at aresumption point in the asynchronous method when the asynchronousoperation completes; return to a calling context after awaitingcompletion of the asynchronous operation; resume execution of theasynchronous method at the resumption point subsequent to completion ofthe asynchronous operation; and use a third member of the awaitableobject to access a result of the asynchronous operation subsequent toresuming execution of the asynchronous method.
 13. The computer programproduct as recited in claim 12, wherein the awaitable object exposes asingle method that calls the first member and the second member, theplurality of other statements being configured to use the single method,instead of using the first member and the second member directly. 14.The computer program product as recited in claim 13, wherein theplurality of other statements are also configured to initialize statedata, including state data for the resumption point, prior to callingthe single method.
 15. The computer program product as recited in claim12, wherein the plurality of other statements are also configured toinitialize state data, including state data for the resumption point,after completion status indicates that the asynchronous operation hasnot already completed and prior to using the second member of theawaitable object to await completion of the asynchronous operation. 16.The computer program product as recited in claim 12, wherein theplurality of other statements are also configured to report to thecalling context that the asynchronous operation has completed whencompletion status indicates that the asynchronous operation has alreadycompleted, and to refrain from use of the second member.
 17. Thecomputer program product as recited in claim 12, wherein the pluralityof other statements are also configured to obtain the awaitable objectby instantiating an instance of the awaitable object.
 18. At a computersystem including one or more processors and system memory, the computersystem also including one or more modules for converting source codeinto executable code, a method for transforming source code to awaitexecution of asynchronous operations, the method comprising: an act ofaccessing an asynchronous method from within a portion of computerprogram source code; an act of recognizing a statement requesting toawait the completion of an asynchronous operation, the statementincluded in the asynchronous method; in response to recognizing thestatement, an act of transforming the statement into a plurality ofother statements, the plurality of other statements configured to use anawaitable object to await completion of the asynchronous operation, theplurality of other statements configured to: use a first member of theawaitable object to determine a completion status of the asynchronousoperation, the completion status selected from among already completedand not yet completed; generate state information when the completionstatus indicates that the asynchronous operation has not yet completed,the state information including establishing a resumption point in theasynchronous method; use a second member of the awaitable object toawait completion of the asynchronous operation when the completionstatus indicates that the asynchronous operation has not yet completed,the second member configured to await completion of the asynchronousoperation and to resume execution of the asynchronous method at theresumption point when the asynchronous operation completes; return to acalling context after awaiting completion of the asynchronous operation;resume execution of the asynchronous method at the resumption pointsubsequent to completion of the asynchronous operation; and use a thirdmember of the awaitable object to access a result of the asynchronousoperation subsequent to resuming execution of the asynchronous method.19. The method of claim 18, wherein the plurality of other statementsare also configured to report to the calling context that theasynchronous operation has completed when completion status indicatesthat the asynchronous operation has already completed, and to refrainfrom generating state information and using second member.
 20. Themethod of claim 18, wherein the awaitable object is a future object,representing one or more future states of the asynchronous operationrunning to completion, the one or more future states including one ormore of: successful completion, exceptional completion, or completiondue to cancellation.